Orthogonal frequency division multiplexing (OFDM) is one of the modulations of choice for high data rate, high performance communications systems. In an OFDM system, bandwidth is divided into closely spaced orthogonal subcarriers, also referred to as tones, which are modulated with data symbols. The transmitted data is divided into several parallel data streams or channels, one for each sub-carrier. Each subcarrier is modulated with a modulation scheme, such as quadrature amplitude modulation or phase shift keying, at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth. An OFDM system is able to eliminate inter-symbol interference (ISI) in channels based on a large bandwidth-delay spread product. This spread enables OFDM systems to cope with severe channel conditions. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to handle time-spreading and eliminate ISI. These advantages simplify equalizer design and have resulted in adoption of OFDM in several standards including: IEEE 802.11a/g/n, IEEE 802.16e, and 3G-LTE.
Typically, in an OFDM system, no data is transmitted on the DC subcarrier. However, injection of a DC component may occur at the receiver due to impairments. OFDM systems require accurate frequency synchronization between the receiver and the transmitter because with frequency deviation, the sub-carriers will not be orthogonal, potentially resulting in inter-carrier interference. The injection of such a DC component in conjunction with any uncertainty in a carrier frequency offset (CFO) may limit performance of a communication system.